Control equipment



June 2, 1942. F. A. HAMILTON, J 2,285,203

GONTROL EQUIPMENT Fil ed 0.01;. 21, 1941 Inventor: Francis A Hamilton JTT,

by .7/ 6. )M q Hi Attorney Patented June 2, 1942 CONTROL EQUIPMENT Francis A. Hamilton, Jr., Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 21, 1941, Serial No. 415,928

11 Claims.

My invention relates to control equipments and particularly to an equipment for controlling the connection between two alternating current sources or systems.

In the case of interconnected alternating current systems each of which comprises one or more generators supplying an independent distribution circuit, if the power transferred over the tie circuit, which interconnects the two systems, is only a small portion of the load on either system, the interruption of the tie circuit results in only a moderate slowing down of the frequency of one of the systems and a moderate speeding up of the frequency of the other system. Therefore, a quick re-establishment of the tie connection between the two systems may result in service being restored before the two systems have pulled very far out of synchronism. However, in case of two systems one of which consists of a large system and the other of which is a small hydroelectric station which normally supplie all or a large portion of its output to the larger system over the tie connection, the interruption of the tie connection results in a very rapid speeding up of the generator in the hydroelectric station. Since, for hydraulic reasons, the governor in the hydroelectric station cannot be arranged to shut off the supply of Water to the prime mover fast enough to prevent this rapid increase in the generator speed, the two systems may be substantially out of phase by the time the tie connection can be automatically re-established.

One object of my invention is to provide an arrangement of apparatus for preventing two alternating current systems from falling too far out of synchronism during the time interval it takes an automatic reclosing circuit breaker equipment to reestablish the connection between the systems after they have been disconnected from each other in response to a fault.

In accordance with my invention, I provide a suitable load, such as a resistor, which is arranged to be connected to the system which loses its load when the interconnection between the two systems is interrupted. This resistor replaces the load which is disconnected from the system by the opening of the tie connection and tends to keep the two systems from falling too far out of synchronism while the tie connection is interrupted. Preferably it is desirable to provide means for adjusting the resistor, during normal operation, in accordance with the load being transmitted through the tie connection, so that the connection of the resistor restores the load on the system to substantially the same value it was at the time the fault occurred.

My invention will be better understood from the following description when taken in connection with the accompanying drawing the single figure of which diagrammatically illustrates a control system for two normally interconnected alternating current systems, and its scope will be pointed out in the appended claims.

In the accompanying drawing, i represents a tie circuit interconnecting two alternating current systems 2 and 3 respectively energized by the sources 4 and 5. In order to simplify the disclosure I have shown single phase circuits, but in actual practice they may be polyphase. The tie circuit l is connected to the system 2 by a circuit breaker 6 which is arranged in any suitable manner so that it is opened automatically in response to a fault on either system and which is automatically reclosed as quickly as possible after it is opened. As shown, the circuit breaker 6 is of the well known latch-closed type comprising a closing coil T for closing the circuit breaker, a latch 8 for holding the circuit breaker closed and a trip coil 9 for releasing the latch 8. For effooting the opening of the circuit breaker 6 when a fault occurs on either system, I have shown an overcurrent relay Iii, which is connected by means of a current transformer I I so as to be energized in accordance with the current flowing through the tie circuit l and which, when energized by a current above a predetermined value, effects the energization of the trip coil 9. For effecting the automatic reclosing of the circuit breaker 6 after it opens, a control relay I2 is arranged to be energized in response to the opening of the circuit breaker 6 and to complete an energizing circuit for the closing coil 1.

For the purpose of this description, it will be assumed that the system 3 is a relatively large system compared with the system 2 and that, when the tie circuit i is in service, a substantial portion of the output of the source 4 is trans mitted over the tie circuit l to the system 3, Therefore, the opening of the circuit breaker 6 effects a substantial reduction in the load on the source 4 which causes the speed of the prime mover driving the source 4 to increase temporarily until the governing means associated therewith can function to restore the speed to its normal value. This rapid change in speed of the generator 4 produces a quick change in the phase relation of the voltages of the disconnected systems 2 and 3 so that by the time the circuit breaker 6 can be reclosed, the voltages may be so far out of phase that the two systems cannot pull into synchronism.

In order to prevent the voltages of the systems 2 and 3 from getting too far out of phase while the circuit breaker 6 is open, I provide a suitable load such as a resistor I4 which is arranged to be connected to the system 2 while the circuit breaker 6 is open. As shown, the resistor 4, which may be of any suitable construction;

such for example as a'liquid rheostat, is arranged to be connected to the system 2 by a circuit breaker I5 of the latch-closed type comprising a closing coil I 6, the circuit of which is arranged to be completed by the overcurrent relay It], a latch I! for holding the circuit breaker closed and a trip coil I8, which is arranged to be energized at the same time the closing coil I of the circuit breaker 6 is energized. The circuit of the trip coil I8 is completed by a control relay I9 which is connected in series with the closing coil 1 of the circuit breaker 6. Preferably the resistor I4 is adjusted so that the amount thereof, which is connected to the system 2 by the circuit breaker I5, is substantially equal to the amount of load being supplied to the system 3 through the tie circuit I at the time a fault occurs. In

'order to accomplish this result, I have shown a wattmetric responsive device 20 connected to the tie circuit'l and arranged to vary, in accordance with the power supplied through the circuit I, the amount of the resistor I4 connected to the system 2 by the circuit breaker I5. Any other suitable power indicating means, such for ex ample as the governor adjustment, may be used.

If the amount of power being furnished to the tie circuit I from the system 2 is relatively small at the time circuit breaker I5 is opened, the reduction in load on the generator 4 effected by the opening of the circuit breaker 5 does not effect a material charge in the speed of the source 4 so that it is not necessary to connect the resistor I4 to the system 2 to prevent the two systems 2 and 3 from getting too far out of synchronism while the circuit breaker 6 is open. Therefore, in the energizing circuit of the closing coil I6 of the circuit breaker I5, I have inserted the contacts 22 of a wattmeter 23 which is connected to the tie circuit I and which is so arranged that the contacts 22 are closed only when the power flow through the circuit I is above a predetermined value for a predetermined time.

If a short circuit occurs in the resistor I4 while it is in service, it is desirable to disconnect the resistor I4 from the source 4 as quickly as possible. In order to avoid the expense of making the circuit interrupter I5 of sufficient capacity to interrupt the short circuit current, I provide an arrangement for opening the circuit breaker 25 which connects the source 4 to system 2 and which normally has to be of sufficient capacity to interrupt all fault currents that may be supplied bythe source 4. As shown, the circuit breaker 25 is provided with a trip coil 26, the energizing circuit of which is arranged to be completed by an overcurrent relay 2! which is connected to the circuit of the resistor I4 by means of a current transformer 28 so that it is energized in accordance with the current flowing through the circuit breaker I5 when it is closed.

In order to prevent the circuit breaker 6 from being reclosed when the source .4 is disconnected from the system 2 due to a fault in the loading.

resistor I4, the overcurrent relay 2'1, when operated, also opens contacts in the energizing circuit Preferably the overcurrent relay 21 is of the well known type which has to be manually reset after each operation thereof.

The operation of the arrangement shown in the drawing is as follows:

During normal operating conditions, the circuit breakers 6 and 25 are closed and the circuit breaker I5 is open, and the wattmetric responsive device 20 varies the resistor I4 in accordance with the amount of power being transferred from the system 2 to the system 3 through the tie circuit I.

When a fault occurs on either system or on the tie circuit I, a sufficient amount of current flows through the tie circuit I to the fault to cause the overcurrent relay in to close its contacts 30 and 3|; The closing of the contacts 30 completes an energizing circuit for the trip coil 9 through the auxiliary contacts 3-2 on the circuit breaker 6 so as to effect the opening thereof and the disconnection of the two systems 2 and'3 from each other. The closing of the contacts 3! of the overcurrent relay Ifl completes an energizing circuit for the closing coil I6 of the circuit breaker I5 through the auxiliary contacts 33 on the circuit breaker I5 and the contacts 22 of the power relay 23 if the power flow through the circuit I is above a predetermined value at the time the fault occurs. The amount of load connected to the system 2 by the closing of the circuit breaker I5 depends upon the position of the wattmetric responsive device 20 at the time the fault occurs. Preferably the circuit breaker I5 is closed and the circuit breaker 6 is opened at as nearly the same instant as possible.

As soon as the circuit breaker 6 opens, its

' auxiliary contacts 34 complete an energizing cirof the closing coil I of the circuit breaker 6.

cuit for the control relay I2 which, by closing its contacts 35, immediately completes an energizing circuit for the closing ccil I through the .auxiliary contacts 36 on the circuit breaker 6,

the winding of control relay II! and the normally closed contacts 31 of the overcurrent relay 21 so that the circuit breaker 6 is immediately re-- closed. The closing of the contacts 38 of the control relay It completes an energizing circuit for the trip coil I8 through the auxiliary contacts 39 on the circuit breaker I5 so as to effect the opening thereof. Preferably the devices are arranged so that the circuit breaker I5 is opened and the circuit breaker 6 is closed at as nearly the same instant as possible.

In case a fault occurs in the resistor I4 while the circuit breaker I5 is closed, the overcurrent relay 21 closes its contacts 40 so as to complete an energizing circuit for the trip coil '26 to effect the opening of the circuit breaker 25 and the disconnection of the source 4 from the system 2. At the same time the overcurrent relay 2! opens its contacts 31. in the energizing circuit of the closing coil I of the circuit breaker 6 so as to prevent the circuit breaker 6 from being reclosed.

While I have, in accordance with the patent statutes, shown and described my invention'as applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, two alternating current systems, a tie circuit connecting said systems,

means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for controlling the load connected to one of said systems so as to prevent said systems from getting too far out of synchronism while said. tie circuit is interrupted.

2. In combination, two interconnected alternating current sources, means responsive to a fault on one of said sources for disconnecting said sources from each other and then quickly reconnecting them together, and means for connecting a sufficient load to one of said sources while they are disconnected to prevent the sources from getting too far out of synchronism before they are reconnected.

3. In combination, two alternating current systems, a tie circuit connecting said systems, means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for preventing said systems from getting too far out of synchronism while said tie circuit is interrupted comprising means for increasing the load connected to one of said systems when said tie circuit is interrupted.

4. In combination, two alternating current systems, a tie circuit connecting said systems, means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for preventing said systems from getting too far out of synchronism while said tie circuit is interrupted comprising a load, and means for connecting said load to one of said systems when said tie circuit is interrupted.

5. In combination, two alternating current systems, a tie circuit connecting said systems, means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for preventing said systems from getting too far out of synchronism while said tie circuit is interrupted comprising a load normally disconnected from one of said systems, and means for connecting said load to said one of said systems when said tie circuit connection is interrupted and for disconnecting said load from said one of said systems when said tie connection is re-established.

6. In combination, two independently energized alternating current systems, a tie circuit interconnecting said systems, a circuit breaker in said tie circuit, a load normally disconnected from said systems, and means for efiecting the opening of said circuit breaker and the connection of said load to one of said systems in response to a fault on said systems and the subsequent reclosing of said circuit breaker and disconnection of said load from said one of said systems.

'7. In combination, two alternating current systems, a tie circuit connecting said systems, means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for preventing said systems from getting too far out of synchronism while said tie circuit is interrupted, and means for connecting to one of said systems while said tie circuit connection is interrupted a load of a value proportional to the load disconnected from said one of said systems by the interruption of said tie circuit.

8. In combination, two alternating current systems, a tie circuit connecting said systems, means responsive to a fault on said systems for interrupting and then quickly re-establishing said tie circuit, and means for preventing said systems from getting too far out of synchronism while said tie circuit is interrupted comprising a load, means for varying the impedance of said load inaccordance with the power flow through said tie circuit, and means for connecting said load to one of said systems while said tie circuit is interrupted.

9. In combination, two independently energized alternating current systems, a tie circuit interconnecting said systems, a circuit breaker in said tie circuit, a load normally disconnected from said systems, means for varying the impedance of said load in accordance with the power flow through said tie circuit, fault responsive means connected to said tie circuit for effecting the opening of said circuit breaker and the connection of said load to one of said systems, and means responsive to the opening of said circuit breaker for effecting a quick reclosure thereof and the disconnection of said load from said one of said systems.

10. In combination, two alternating current systems, a source connected to one of said systems, a tie circuit connecting said systems, a load normally disconnected from said systems, means responsive to a fault on said systems for effecting the opening of said tie circuit and the connection of said load to said one of said systems and the subsequent re-establishment of said tie connection and the disconnection of said load from said one of said systems, and means responsive to a fault in said load while connected to said one of said systems for effecting the disconnection of said source from said one of said systems.

11. In combination, two alternating current systems, a source connected to one of said systems, a tie circuit connecting said systems, a load normally disconnected from said systems, means responsive to a fault on said systems for effecting the opening of said tie circuit and the connection of said load to said one of said systems and the subsequent re-establishment of said tie connection and the disconnection of said load from said one of said systems, and means responsive to a fault in said load while connected to said one of said systems for effecting the disconnection of said source from said one of said systems and for preventing the subsequent re-establishment of said tie connection.

FRANCIS A. HAMILTON, J R. 

